DAYTONA BEACH, Fla.—Denny Hamlin has had back issues for the last four years.

This week, that issue turned into a problem.

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A bulging disk and a torn disk in his back forced him to sit out Sprint Cup practice Thursday at Daytona International Speedway in addition to giving up his seat in Friday's Nationwide Series race.

Hamlin said he would have tried to practice at any other track but with the limited amount of input a driver has at Daytona, it made more sense to sit out and not risk aggravating the injury.

The back issues, which he said are genetic, were aggravated last week at Kentucky Speedway, where the track is quite bumpy. He underwent an MRI this week and said he was told any surgery would be “years down the road” and therapy should take care of his problems.

“The next day (after Kentucky), it just got real tight by the end of the day and then I sat down for dinner and couldn’t get up,” Hamlin said Thursday night. “I’ve had a history of back spasms now for probably four years and it just flared up again.

“This is about as bad as it was at its worst in 2008. I’m just now starting to get mobile again and get around.”

The Joe Gibbs Racing driver, who will be replaced by Clint Bowyer in the Nationwide race, said he doesn’t plan to have a backup driver for the Coke Zero 400 on Saturday.

Hamlin, who is fifth in the Cup standings, must qualify the car Friday in order to start where the car qualifies and must start the car Saturday in order to be credited with the points for the event.

There’s no requirement for him to practice, but the car must be practiced or NASCAR could choose to keep the car out of the race or force it start in the rear.

Kyle Busch practiced Hamlin’s car for three laps and the team called it a day.

“With spasms, … anything can set it off,” Hamlin said. “Obviously, the most risk of having an accident in practice would be on a superspeedway and the likelihood of me getting in an accident in the Nationwide race would be very high as well and those are things that could trigger me going backwards from everything I’ve gained this week.

“Nine times out of 10 the best you’re going to be is the way you unloaded anyway. We’re confident that what we had in February will be fine for Saturday night and we just wanted to minimize risk.”

Hamlin said he didn’t know if his active lifestyle—he enjoys basketball and golf—has aggravated the problems but he will have to temporarily stop doing those things.

“We’re just doing a lot of ice and (electrical) stim and rehab and stuff like that that I’m going to have to continue to do for a while,” Hamlin said. “Having a couple of needles in my spine this morning was not the best feeling. It was good I could get a day off.”

The 31-year-old driver hopes he can get back to normal—meaning where he deals with a sore back but not to the extent the last few days—by early next week.

“We really know now exactly what’s going on,” Hamlin said. “Now we know how to treat it. This is something I just let go away in 2008 or whatever when it happened the first time.”